Permanent magnet alternators, which can include similarly designed magneto alternators, have permanent magnets assembled on the inner walls of a rotor, for example, formed as a flywheel. The permanent magnet alternator may include a stator positioned inside the rotor or a flywheel magneto ignition system. Typically the stator has a plurality of coils that produce the alternating current, voltage and power used for charging, ignition and lighting systems. Different coils and magnets can be configured to increase alternator output, which includes a design known as a dual-rate alternator. Many of the permanent magnet alternators are single-phase and use one charging coil to output a single-phase AC wave through stator output terminals. The output frequency depends on the number of magnets assembled on the rotor. The similarly designed flywheel magneto ignition system uses a self-contained ignition system to deliver a high voltage spark.
Permanent magnet alternator systems are used on marine outboard motors, motorcycles and similar small engines. The voltage regulators used with such systems typically use open loop control instead of the more common closed loop control systems used on automobile systems. These open loop regulators are more simple, less complex, cost less, and thus, are more adapted to smaller outboard and motorcycle engines.
These regulators often include a rectifier circuit, for example, using silicon controlled rectifiers and a diode bridge circuit operative with the silicon controlled rectifiers. The alternator system, voltage regulator and battery could be designed to be series connected, or designed as a shunt system. A drawback of these regulators, however, was overheating. As engine RPM increases and the alternator spins at higher RPM's, the voltage increases, sometimes reaching as high as 250 volts peak, i.e., 500 volts peak-to-peak, causing extreme overheating and burn-up of the voltage regulator. Some proposed alternator systems, for example, in U.S. Pat. No. 5,078,627, have used a bimetallic switch that was operative to disable the voltage regulator and its rectifier and prevent excessive heating of any electronic components when the ambient temperature within the voltage regulator exceeded a predetermined value. A bimetallic or other mechanical switch, however, is not always reliable and it operates as a mechanical structure only. Bimetallic switches can easily fail depending on their design.